The accurate detection of data is an important aspect of utilizing data stored on a medium. If the data channel responsible for detecting the binary data stored on a storage medium, such as a magnetic tape or disk, cannot accurately detect and output an accurate binary digital equivalent, then the digital system that is to utilize such data is severely handicapped. In general, incorrect and/or inefficient channel detection of binary data stored on media can be due to a number of factors including media defects, hardware/software data channel processing errors, and/or improper setting of channel parameters.
With regard to media defects, these can cause signal drop-ins or drop-outs that may affect the accuracy of binary data detection. Since binary ones are typically associated with high amplitude analog signal portions and zeros with low amplitude analog signal portions, media defects may cause binary values that ought to be detected as binary zeros to be inaccurately detected as binary ones (i.e. drop-in). Conversely, media defects may cause binary ones to be inaccurately detected as binary zeros (i.e. drop-out). Signal drop-outs can occur regularly on magnetic tapes. Thus, if the data channel includes a magnetic tape drive, even "good tapes" can have 10-20% of the information on the tape associated with signal drop-outs.
In the latter two cases, i.e. channel errors and parameter settings, substantial costs are incurred in determining channel performance bottlenecks and anomalies during development, manufacturing and, in particular, once a channel is installed at a customer site. For example, if the data channel includes a magnetic tape drive, it is costly to determine appropriate drive parameter settings to reach a balance between overly accurate data detection where too many re-analyses and read retry requests are generated, and potentially inaccurate data detection where detection errors are not flagged for re-analyses and/or re-read. If the balance is too far in the direction of the former, the channel will be overly slow. If, on-the-other hand, it is too far in the direction of the latter, it will be inaccurate. This balance may be especially costly when the settings must be made on drives located at a customer site. Also, it is crucial from a customer's perspective to identify and solve problems before any data is lost or the data channel decoding rate is greatly slowed by read retries.
Diagnosing channel performance problems, such as those above, effectively and efficiently has been elusive. It would be advantageous to have highly efficient channel evaluator techniques that sample the channel data at one or more steps during channel signal processing and output the necessary information that would allow further analysis, such as when detection accuracy is in question or when channel diagnostics are being executed. The present invention derives its novelty from the use of such channel evaluators, denoted "detection margins," which measure the quality of the data detection. Such detection margins can be obtained during normal operation of the data channel or during diagnostic testing. During normal operation only those portions of the channel data that have a relatively high probability of being erroneous are flagged for subsequent analysis. By placing the channel in a diagnostic mode and attempting to detect binary data on a medium designed to contain diagnostic data, the detection margins can be used to construct a model of the channel. By analyzing the model and its behavior, channel bottlenecks can be identified and corrective action can be taken.